Single use equipment alternatives provide a number of advantages for various industries. Typically, such equipment need not be cleaned and/or stored after use. Single use equipment can also reduce the machinery required for an industrial plant, for example sterilization equipment is not necessary. Further, single use equipment only requires manufacture to withstand a single use, often allowing for alternative, less expensive, material construction. Additionally, initial conditions provided by the manufacturer of such equipment, such as pre-sterilization, for example, can allow the single use equipment to be used without significant setup time or expense. One example of single use equipment is a single use container, such as a single use bioreactor.
Bioreactors are useful for generating and supporting biological reactions for any number of purposes. As a biological reaction progresses, the reaction itself may change a pH of the solution within the bioreactor. Monitoring or detecting pH can thus be highly useful in order to monitor the status and/or progression of a reaction. Accordingly, pH sensors are often used with single use bioreactors.
Detecting a pH of a reaction mixture is one of the most common process chemical measurements, particularly in the biologics industry. pH is a measure of a relative amount of hydrogen and hydroxide ions in an aqueous solution. In fermentation and cell culture, one of the most critical process challenges is to maintain an optimal pH level. Some biologic reactions, such as fermentation or culture processes, utilize a live organism such as a yeast, bacteria, or fungus strain to produce a desired active ingredient. Fermentation processes normally have a relatively short duration (2-7 days). Cell culture is a process in which a mammalian cell is grown to produce an active ingredient. The cell culture typically takes somewhat longer (2-8 weeks). The pH of a reaction mixture for these, or other example biologic reaction processes, often needs to be kept within an optimal range. The mixture becoming too acidic or too basic, for example, may result in a change in the reaction rate, production of unwanted byproducts or even premature death of the live organism driving the reaction.
One significant challenge for pH measurement in the fermentation and cell culture fields is the cleaning processes involved with the fermentation chamber or bioreactor. A fermentation or bioreaction chamber must be sterilized prior to a reaction process to ensure against cross-batch contamination of any unwanted growths. In addition, pH sensors typically undergo a two-point calibration using buffer solutions. Such cleaning can include steaming the fermenter or bioreactor as well as the pH sensor. Exposure to high temperatures, steam and rapid thermal shock can significantly affect the sensor's life.